Apparatus for drying fibrous materials



APPARATUS FOR DRYING FIBROUS MATERIALS Filed DBC. 16, 1929 luluhlulh Patented Feb. 23, 1932 UNITED srr.\.'rla:s` PATENT oFl-ica .ELTON B. DARLING', 0F DANiVILLE, ILLINOIS, ASSIGNOB T0 OQRNSTALK PRODUCTS COMPANY, INC., OF DANVILLE, ILLINOIS, A CORPORATION F DELAWARE APPARATUS son DBYING mnous MATERIALS Application led December 16, 1929. Serial No. 414,466.

The present invention relates to an improvement in diying fibrous material.

One of the ob]ects of the invention 1s the preparation Iof high-alpha cellulosic pulp 1n 5 a particularly suitable form for esterification or for use in the manufacture of artlficial silk and the like.

Hi h-alpha pulp is simply a trade designation 01` a cellulosic pulp of such characteristics that it will substantially withstand the action of 'a cold 171% solution of sodium hydroxide, such as is used in preparing alkalicellulose crumbs for the preparation of cellulose Yxanthogenate in the viscose process. rihis means that cellulose having a high alpha content will not substantially dissolve in such caustic soda solutions. It has been found that high-alpha cellulose is also very suitable for nitration, acetation and for conao version into cellulose ethers and other compounds. rlhe recent great expansion in the utilization of cellulose and its compounds has created a reat demand for cellulose having a relative y high (above 90%) alpha cellulose content. In the past most of this demand has been met by the preparation of high alpha cellulose from cotton linters and cotton waste, although recently high-alpha pulps derived from sulite wood-pulp have 3o appeared .on the market.

A still more recent development has been the preparation of high-alpha cellulosic pulps from farm-wastes such as cornstalks, bagasse, rice-straw, wheat-straw, etc. One

of these modern processes of manufacturing high-alpha cellulosic pulp forms the subject matter of my co-pending application Serial No. 385,061, led August 10, 1929, in which i have described the treatment of cornstalk cellulose with cold 6% sodium hydroxide solutions, whereby constituents other than high-alpha cellulose are removed from the pulp, leavingthe desired high-alpha cellulose therein.

lt has now been found that when washing the alkali-treated cellulose, that the same can very conveniently be sheeted on a paper machine according to standard procedure.

However, when drying such a sheet of highalpha cellulose in the ordinary way, it compacts and becomes very* hard, so that when v it is subsequently desired to acetate, nitrate or otherwise to convert the sheet of highalpha cellulose it is quite resistant to penetration by the reagents employed for carrying out sueh conversion.

The present invention,` therefore, has for one ofits objects a new method lof treating the sheeted high-alpha cellulose while still containing considerable moisture, so as to remove this moisture by means of the vapors of a volatile solvent that has the properties of ventrajning water-vapor.

Among the solvents suitable yfor this purpose are benzene, benzine, acetone, and the volatile alcohols, especially ethyl alcohol, the latter on account of its cheapness and ready recoverability being perhaps the best for the purpose. In the description hereinbelow it will-be assumed that alcohol is the liquid employed, although the invention is most defintely not limited to the use of alcohol as such. Even suitable mixtures of solvents, such as a mixtureof benzene and alcohol may be employed with success. a

Essentially the new method that forms the subject matter of the present invention consists in advancing a continuous web of wet high-alpha cellulose, vor other fibrous material requiring drying through a heated zone while supported by an endless belt of absorbent material that is wet with a volatile liquid. The said belt is in contact, or in very close proximity to, a suitable heater, whereby the volatile liquid absorbed by the belt will be volatilized and driven into the web of high-alpha cellulose or other brous material supported by the belt. A suitable hood, provided with draft or suction-producing means surmounts the heated zone through which the web of fibrous material and the belt travel, thereby providing means for carrying the vapors of the volatile liquid arising from the belt throughvthe web of fibrous material, whereby the water contained in the latter is likewise drivenoff. The combined solvent and water vapors are then conducted from the hood to a suitable condenser or absorbing tower in' which the volatile solvents and Water vapor are vcondensed to form solvent or a 100 alcohol) will also serve, but because of its more or less poisonous nature is not preferred. Acetone will also do, but is somewhat more expensive. Benzene, especially in admixture with alcohol, also is suitable, but complicates the solvent-recovery problem, and, moreover, benzene vapors are poisonous. For the aforesaid reasons, I prefer to operate with ordinary commercial denatured alcohol.

Referring nowr to the drawing forming part of the present application:

A suitable container 10, preferably in the form of a fiat trough, is partially filled with the volatile liquid (alcohol) 11. Suitably mounted in the trough are rollers 12, upon which an endless belt 13 of absorbent material, such as felt, travels. Means, (not shown) for propelling the belt are likewise provided. Placed above the level of the liquld in the trough 10 is a suitable heater 14. This may consist of a hollow metallic box through which steam or hot water is passed -or it may be an electrically heated plate. The belt 13 preferably is closely enough positioned to the heater to insure the volatilization of the liquid absorbed and carried thereby. It is .not absolutely necessary that the belt actually make contact with the heater, althou h such construction will be considered as witin the scope of my invention.

Suitably supported by, for example rollers 15, there arrives a wet web 16 of fibrous material, for exam le, high-alpha cellulose, containing about 0% of water in the form of moisture. The speed of the advancing web of ibrous material (travelling in the direction of the arrows on the drawing) is so adjusted that it coincides with the peripheral speed of the travelling belt 13, so that the belt and the web which is superimposed thereon as shown will travel along over the heater 14 simultaneously and at the same speed.

The amount of volatile liquid (alcohol) carried by the 4belt 13 may be adjusted by tightening or loosenin the squeeze rollers 17. Under the influence o the heat arisin from the heater 14, the volatile liquid in t e belt will be volatilized and will escape upwardly into the web of wet fibrous material. At the same time the water contained in the web of material will come under the influence of the hot vapors of liquid and will-therefore be entrained by the latter and thus likewise volatilized and removed from the web of material. This procedure is accelerated and aided by .provided with an exit pipe 2O leading to a solvent recovery apparatus (not shown). The course of travel of the water vapors and v liquid vapors is indicated by the wavy arrows in the hood and exit ipe.

After the web of ce lulose leaves the belt it is transported on rollers 21 and eventually is rolled up and forms an article of commerce in that form. Alternatively thec web may be cut into suitable lengths, or may pass into a machine in which it is broken up and made still more fluffy by mechanical means such as tearing, teasing, etc.

When drying alpha cellulose by the method hereinabove described, it forms a very loose, soft mass that has very much the appearance of cotton batting. It lends itself most readily to acetation, nitration and the other processes for the conversion of cellulose into its derivatives.

The present method of drying cellulosic webs differs from the older known methods of dehydrating cellulose esters in which alcohol is employed for the physical displacement of water. For example, in the manufacture of smokeless powder from cellulose nitrate, the thoroughly boiled, poached and stabilized cellulose nitrate, in finely divided form, is highly compressed in hydraulic presses to form what is technically termed a cheese of compressed water-wet cellulose nitrate. Ordinary alcohol is then mechanically forced throu h the compressed mass of the cheese where y the water therein contained is actuall physically propelled through the cheese be ore the advancing mass of alcohol. The

liquid coming from the apparatus is tested from time to time, and when the specific gravity thereof shows that it is pure alcohol, then the operator of the apparatus thereby is informed that all of the water has been removed from the mass of cellulose nitrate. This is a very elicient and safe way of drying cellulose nitrate, but is entirely due to the mechanical displacement of the water by alcohol, as no heat whatever is usedin fact heat at this stage would be very dangerous. My purpose in describing this method of drying cellulose nitrate is to point out that my improved method of drying an advancing web of cellulose is essentially different from the method of forcing water out of wet cellulose nitrate. As, however, my improved method of drying cellulosic webs is also applicable to the drying ofwebs of other than alpha cellulose; for example, may serve -for the` drying of an advancing web of cellulose nitrate (if the temperature is kept low enough), or of an advancing web of a cellulose ester in fibrous form, I do not wish to be limited to the mere drying of high-alpha cellulose by my method. Any

suitable ibrous material may be dried in this manne-r.

While I have shown one means of appl ing volatile vapors to the web of material, it 1s an obvious expedient to replace the belt by a perforated or otherwise porous plate or sheet or by passing preliminarily volatilized alcohol thrlough the advancing web of fibrous mater1a With only the 'above limitations, andv withholding for myself such obvious changes or minor mechanical improvements as may suggest themselves to those skilled in the art into which this invention falls, I desire to protect by Letters Patent of the United States of America the following:

1. Apparatus for drying a web of fibrous material which comprises a container for con- -taining a volatile liquid, belt-supporting means in said container, an v absorbent belt travelin over said means and fora portion of its lengt so arranged as to be below the level of said liquid, a heater over which a portion of the belt above the-liquid travels, means for applying a web of wet fibrous material to the surface of said belt on the side thereof awa from said heater, and means above saidvweii and belt for withdrawing vapors arising from said belt and web.

2. In an apparatus as delined in claim 1,

whereinvmeans are provided for regulating il'gh amount of volatile liquid absorbed by the e t.

3. Apparatus for drying a web of fibrous material which comprises an means for propelling the same, plying volatile liquids to said belt, a heater over which said belt may pass, means for applying a web of fibrous material to the belt, and means -for withdrawing vapors'from the zone of the belt above said heater.

4. `Apparatus for drying a web of fibrous material which comprises means for continuously moving said web means for applying vapors of a volatile li uid to said 'web while so moving, and means or causing said vapors to pass through said web and for conducting said vapors away with entrained moisture from said web.

In witness whereof, I have hereunto subscribed my name.

- ELTON R. DARLING.

means for apendless belt, I 

